Catalyst comprising a group VIB metal carbide, phosphorous and its use for hydrodesulphurisation and hydrogenation of gas oils

ABSTRACT

The invention concerns a catalyst containing at least one amorphous oxide matrix, at least one carbide and phosphorous deposited on said catalyst or contained in the matrix, in which the carbide contain at least one group VIB element and, optionally, at least one element from group VIII of the periodic table. The invention also concerns the use of the catalyst for hydrodesulphurisation and hydrogenation of aromatic compounds in gas oils with a low sulphur content.

This application claims the benefit of the filing date of U.S.Provisional Application Ser. No. 60/158,123 filed Oct. 8, 1999.

The present invention relates to a catalyst containing a carbide of atleast one group VIB metal and phosphorous on an amorphous support, andto the use of this catalyst for hydrotreatment ofhydrocarbon-containing, feeds with low sulphur contents.

The present invention also relates to the field of fuel for internalcombustion engines, more particularly the manufacture of a fuel for acompression ignition engine from a novel hydrotreatment catalyst phase.

Gas oil cuts, whether from distillation or from a conversion processsuch as catalytic cracking, currently contain non negligible quantitiesof aromatic, nitrogen-containing, and sulphur-containing compounds. Thecurrent legislation of the majority of industrialised countries requiresthat fuel which can be used in engines must contain less than 500 partsper million by weight (ppm) of sulphur. In the very near future, thismaximum quantity will be reduced to 350 ppm in about 2000 and to 50 ppnmin about 2005 for the member states of the European Community. Regardingthe amount of polyaromatic compounds in gas oils, this may be reduced toa very low value (of the order of 1% to 2%) from 2005. In this context,hydrogenation of the polyaromatics contained in gas oil cuts is thusincreasing in importance, because of the new sulphur and aromaticcompound limits in this type of fuel.

Desulphurisation is generally carried out under conditions and usingcatalysts which are not capable of simultaneously carrying outhydrogenation of the aromatic compounds. Thus a first treatment of thecut must be carried out to reduce the sulphur content followed by asecond treatment to hydrogenate the aromatic compounds contained in thecut. This second step is generally carried out by bringing the cut, inthe presence of hydrogen, into contact with a catalyst generally basedon a noble metal. However, because the desulphurisation process cannever completely eliminate the sulphur-containing andnitrogen-containing compounds, the catalysts used must be able tooperate in the presence of such compounds, which are powerful inhibitorsof the activity of noble metals. It is thus important to seek out activephases having good thio-resistant properties. The aim of the presentinvention is thus to discover a novel catalyst based on a carbide whichcould be substituted for the noble metals used by the skilled person.

The use of massive or supported group VIB carbides as hydrotreatmentcatalysts for certain reactions on a model or actual feed has alreadyformed the subject matter of prior art publications (S. T. Oyama et al.,in Catal. Today, 15 (1992) pp. 179-200, or App. Catal., 168 (1998), pp.219-228 and App. Catal. A., 134 (1996), pp. 339-349).

The Applicant has discovered that surprisingly, the introduction of aquantity of phosphorous can substantially improve the activity of acatalyst containing at least one carbonized group VIB metal on anamorphous oxide support, preferably alumina or silica-alumina. Further,the activity of the catalyst is better if during preparation of thecatalyst, a heteropolyanion type compound containing at least one groupVIB element, phosphorous and group VIB elements introduced by anyprecursor is preferentially used. The catalyst can optionally contain atleast one element from group VIII of the periodic table. Such a catalystcan advantageously carry out hydrodesulphurisation and hydrogenation ofaromatic compounds in hydrocarbon-containing feeds containingsulphur-containing compounds.

The invention also concerns the use of said catalyst for treatinghydrocarbon-containing cuts containing sulphur and aromatic compoundsand more particularly gas oil cuts from distilling crude oil and avariety of conversion processes such as cuts known as “cycle oils” fromcatalytic cracking processes. The catalyst of the present invention canbe used for desulphurisation and hydrogenation of hydrocarbon-containingcuts. The feed which can be treated using the process of the inventionhas sulphur contents of less than 2000 ppm by weight, preferably 0.01 to500 ppm by weight. However, this catalyst can also be suitable for anyprocess aimed at hydrogenating all or a portion of the aromaticcompounds of a feed containing traces of sulphur-containing compounds,such as hydrogenation of aromatic compounds in edible oils and insolvents.

The catalyst of the present invention generally comprises, in weight %with respect to the total catalyst weight:

0.1% to 30% of a carbide phase containing at least one group VIB elementwith formula MxCy where M is at least one group VIB element and theratio y/x is in the range 0.75 to 0.25;

01% to 10% of phosphorous; and optionally:

0 to 10% of at least one metal from group VIII of the periodic table.

Thus the catalyst comprises phosphorous and a group VIB metal, such thatthe preferred P/VIB metal mole ratio is in the range 0.05 to 1.2, morepreferably in the range 0.08 to 0.55.

The catalyst is characterized in that the carbide phase is in the formof small particles with a size of less than 80 Å, preferably less than50 Å and more preferably less than 30 Å.

The catalyst of the present invention can be prepared using any methodwhich is well known to the skilled person. Preferably, the catalyst ofthe present invention can be obtained using the following steps:

a) impregnating a solution into an amorphous oxide matrix, said solutioncontaining at least one group VIB element, phosphorous and optionally agroup VIII element. Preferably, a salt of a heteropolyanion containingat least one group VIB element and phosphorous and optionally at leastone group VIII element more generally with formula AxByCzO_(n) is used,where A is at least one group VIB element, B is a group VIII element, Cis phosphorous and O is oxygen, where the ratios z(x+y) can be in therange 0.05 to 1.2, preferably in the range 0.08 to 0.55,

b) optionally, drying;

c) optionally, activating the catalyst in an oxidising or neutralmixture,

d) optionally, carrying out a reduction step;

e) carbonization with a hydrocarbon;

f) optionally, passivating in an inert gas plus oxygen.

Impregnation step a) can be carried out using any method which is wellknown to the skilled person. The components constituting the catalystcan be introduced separately into the catalyst, in successive additionsteps using solutions of one or more elements, or simultaneously using acommon solution of the elements. When a plurality of impregnation stepsare carried out to produce the catalyst, drying or activation (calciningor reduction) steps can be carried out between two successiveimpregnation steps.

Drying step b) can be carried out using any method which is well knownto the skilled person, at a maximum temperature of 150° C.

Activation step c) consists of calcining in a neutral or oxidisingmixture using any method which is well known to the skilled person at atemperature of more than 100° C. and less than 900° C.

Reduction step d) consists of reduction in pure hydrogen or hydrogenmixed with an inert gas (for example argon) at a temperature of morethan 100° C. and less than 900° C.

Carbonization step e) is carried out in two parts. A first part consistsof placing the catalyst in an inert atmosphere (for example under argon)up to temperatures of 400° C. or 500° C. depending on the group VI metalused. The second part (the carbonization step proper) consists ofcarbonizations preferably using a programmed temperature profile in ahydrocarbon/hydrogen mixture (for example a mixture of 20% methane orany alkane, alkene or alkyne used pure or as a mixture and with thecomplement to 100% of hydrogen) to final temperatures of 677° C. to 850°C. Depending on the metal used, a final constant temperature stage isnecessary to obtain a catalyst with good catalytic properties.

Step f) is a passivation step. Since this type of catalyst can bepyrophoric, a supplemental step is then necessary to avoid totaloxidation of this catalyst. This step is generally carried out atambient temperature (25° C.) by placing the catalyst under an inert gasthen adding a low partial pressure of oxygen to that gas (1%) forperiods of 1 to 15 hours.

The amorphous oxide matrix is selected from transition aluminas, silicasand silica aluminas and mixtures thereof. This type of support has aspecific surface area, determined using techniques which are known tothe skilled person, in the range 100 to 600 m²/g, preferably in therange 150 to 500 m²/g. The amorphous oxide support can be used in theform of a powder or pre-formed in the form of beads or extrudates.

Sources of group VIB elements which can be used are well known to heskilled person. As an example, preferred sources of molybdenum andtungsten which are used are oxides and ammonium salts are used such asammonium molybdate, ammonium heptamolybdate and ammonium metatungstate.Preferably, salts of heteropolyacids of group VIB metals such asphosphomolybdic acid or phosphotungstic acid are used.

The precursors of group VIII metals which can be used are well known tothe skilled person. As an example, for non noble metals, nitrates,sulphates, phosphates, halides, for example chlorides, bromides andfluorides, or carboxylates, for example acetates and carbonates, areused. For the noble metals nitrates are used when they exist, halides,for example chlorides, nitrates, acids such as chloroplatinic acid, orchloroiridic acid, alkali metal chlorometallates, chloro-orhydroxo-amminated complexes, or oxychlorides such as ammoniacalruthenium oxychloride. It is also possible to use soluble co-ordinationcomplexes in organic solvents, such as acetylacetonate complexes. It isalso possible to use carbonyl complexes.

Preferably, the group VIII metal is selected from non-noble metals andpreferably from nickel and cobalt.

The hydrocarbons used for the carbonization step can be selected fromalkanes, alkenes, alkynes, aromatic compounds or any otherhydrocarbon-containing compound which is well known to the skilledperson for its carbonizing properties. These hydrocarbons can be mixedwith an inert gas or with hydrogen.

The hydrodesulphurisation process of the invention is generally carriedout at temperatures of 100° C. to 400° C., preferably 150° C. to 380° C.The operating pressure is generally 0.1 to 30 MPa, preferably 1 to 20MPa. The space velocity, expressed as the volume of liquid feed treatedper volume of catalyst per hour, is generally 0.1 to 20 h¹⁻. Thehydrogen/feed ratio used is expressed as the volume of hydrogen measuredunder normal conditions per volume of liquid feed; it is generally 50/1to 2000/1.

The feeds used generally contain at least 10% of aromatic compounds andless than 2000 ppm of S. They may be kerosines or gas oils fromatmospheric distillation or feeds originating from refining processessuch as catalytic cracking, coking, visbreaking, and hydroconversion ofresidues.

The following non limiting examples illustrate the invention.

EXAMPLE 1

Preparation of an Alumina Support

We produced large quantities of an alumina-based support so as to beable to prepare the catalysts described below from the same formedsupport. To this end, we used a matrix composed of ultrafine tabularboehmite or alumina gel sold by Condea Chemie GmbH under the trade nameSB3. This gel was mixed with an aqueous solution containing 66% nitricacid (7% by weight of acid per gram of dry gel) then mixed for 15minutes. Following mixing, the paste obtained was passed through a diewith cylindrical orifices with a diameter of 1.3 mm. The extrudates werethen dried overnight at 120° C. and calcined at 550° C. for 2 hours inmoist air containing 7.5% by weight of water. Cylindrical extrudates 1.2mm in diameter were thus obtained, with a specific surface area of 243m²/g, a pore volume of 0.61 cm³/g and a unimodal pore size distributioncentred on 10 nm. X ray diffraction analysis of the matrix revealed thatit was solely composed of low crystallinity cubic gamma alumina.

EXAMPLE 2

Preparation of Sulphurised Mo and CoMo Catalysts (not in Accordance withthe Invention)

Thirty grams of the alumina support of Example 1 were impregnated bynascent humidity, in one step, from a solution of ammoniumheptamolybdate so as to deposit 13.5% by weight of MoO₃ on the aluminasurface. After ageing, this sample was oven dried overnight at 80° C.The sample then underwent calcining in dry air at 500° C. for two hours.The catalyst was then sulphurised with a H₂/H₂S mixture containing 15%by volume of H₂S at 350° C. for 2 hours. Reference catalyst Mo-S wasthus obtained.

A sulphurised MoP/alumina catalyst was then prepared. Thirty grams ofthe alumina support of Example 1 were impregnated by nascent humidity,in one step, from a solution of ammonium heptamolybdate and phosphoricacid so as to deposit 13.5% by weight of MoO₃ and 2.66% by weight ofP₂O₅ on the alumina surface. After ageing, this sample was oven driedovernight at 80° C. The sample then underwent calcining in dry air at500° C. for two hours. The catalyst was then sulphurised with a H₂/H₂Smixture containing 15% by volume of H₂S at 350° C. for 2 hours.Reference catalyst MoP-S was thus obtained.

A sulphurised CoMo/alumina catalyst was then prepared. Thirty grams ofthe alumina support of Example 1 were impregnated by nascent humidity,in one step, from a solution of ammonium heptamolybdate and cobaltnitrate so as to deposit 13.5% by weight of MoO₃ and 2.66% by weight ofP₂O₅ on the alumina surface. After ageing, this sample was oven driedovernight at 80° C. The sample then underwent calcining in dry air at500° C. for two hours. The catalyst was then sulphurised with a H₂/H₂Smixture containing 15% by volume of H₂S at 350° C. for 2 hours.Reference catalyst CoMo-S was thus obtained.

A sulphurised CoMoP/alumina catalyst was then prepared. Thirty grams ofthe alumina support of Example 1 were impregnated by nascent humidity,in one step, from a solution of ammonium heptamolybdate, cobalt nitrateand phosphoric acid so as to deposit 13.5% by weight of MoO₄,4% byweight of CoO and 2.66% by weight of P₂O₅ on the alumina surface. Afterageing, this sample was oven dried overnight at 80° C. The sample thenunderwent calcining in dry air at 500 ° C. for two hours. The catalystwas then sulphurised with a H₂/H₂S mixture containing 15% by volume ofH₂S at 350° C. for 2 hours. Reference catalyst CoMoP-S was thusobtained.

EXAMPLE 3

Preparation of Carbonized Mo and CoMo Catalysts (not in Accordance withthe Invention)

Thirty grams of the alumina support of Example 1 were impregnated bynascent humidity, in one step, from a solution of ammoniumheptamolybdate so as to deposit 13.5% by weight of MoO₃ on the aluminasurface. After ageing, this sample was oven dried overnight at 80° C.The sample was then removed for carbonizing as follows: the temperaturewas raised at 60° C./h to 400° C. in argon to dry and reduce thecatalyst, followed by a carbonizing step at a programmed temperatureprofile of 30° C./h to 677° C. in a stream of methane at atmosphericpressure. The catalyst was then cooled in a stream of argon to ambienttemperature then treated in a stream of argon and 1% of oxygen for 15hours to passivate it. Reference catalyst Mo-C was thus obtained.

A carbonized CoMo/alumina catalyst was then prepared. Thirty grams ofthe alumina support of Example 1 were impregnated by nascent humidity,in one step, from a solution of ammonium heptamolybdate and cobaltnitrate so as to deposit 13.5% by weight of MoO₃ and 4% by weight of CoOon the alumina surface. After ageing, this sample was oven driedovernight at 80° C. The sample was then removed for carbonizing asfollows: the temperature was raised at 60° C./h to 400° C. in argons todry and reduce the catalyst, followed by a carbonizing step at aprogrammed temperature profile of 30° C./h to 677° C. in a stream ofmethane at atmospheric pressure. The catalyst was then cooled in astream of argon to ambient temperature then treated in a stream of argonand 1% of oxygen for 15 hours to passivate it. Reference catalyst CoMo-Cwas thus obtained.

EXAMPLE 4

Preparation of Carbonized MoP/alumina and CoMoP/alumina (in Accordancewith the Invention)

A catalyst was prepared in the same manner as that described for Example3 by impregnating the alumina of Example 1 with a solution of ammoniumheptamolybdate and phosphoric acid so as to deposit 13.5% by weight ofMoO₃ and 2.66% by weight of P₂O₅ on the alumina surface. The noncalcined sample underwent the same ageing, drying, carbonizing andpassivation treatment as the sample of catalyst Mo-C of Example 3.Catalyst MoP-C was thus obtained.

Catalyst CoMoP was then prepared. In the same manner as that describedfor Example 3, the alumina of Example 1 was impregnated with a solutionof ammonium heptamolybdate, cobalt nitrate and phosphoric acid so as todeposit 13.5% by weight of MoO₃, 4% by weight of CoO and 2.66% by weightof P₂O₅ on the alumina surface. The non calcined sample underwent thesame ageing, drying, carbonizing and passivation treatment as the sampleof catalyst Mo-C of Example 3. Catalyst CoMoP-C1 was thus obtained. XRDanalysis revealed that the catalyst contained no carbide particles witha size greater than 80 Å.

EXAMPLE 5

Preparation of a Carbonized MoP/alumina Catalyst (in Accordance with theInvention)

In the same manner as that described for Example 4, a catalyst wasprepared from the alumina of Example 1 by impregnation with commerciallyavailable phosphomolybdic acid H₃PMo₁₂O₄₀ solution. The non calcinedsample underwent the same ageing, drying, carbonizing and passivationtreatment as catalyst Mo-C of Example 3. Catalyst MoP-C2 was thusobtained. XRD analysis revealed that the catalyst contained no carbideparticles with a size greater than 80 Å.

EXAMPLE 6

Preparation of a Carbonized MoP/alumina Catalyst (in Accordance with theInvention)

In the same manner as that described for Example 4, a catalyst wasprepared from the alumina of Example 1 by impregnation with awater-soluble heteropolyanion (NH₄)₆P₂Mo₅O₂₃. A portion of the samplewas dried then underwent the same ageing, drying, carbonizing andpassivation treatment as the sample of catalyst Mo-C of Example 3.Catalyst MoP-C3 was thus obtained. XRD analysis revealed that thecatalyst contained no carbide particles with a size greater than 80 Å.

EXAMPLE 7

Preparation of a Carbonized MoP/alumina Catalyst (in Accordance with theInvention)

In the same manner as that described for Example 4, a catalyst wasprepared from the alumina of Example 1 by impregnation with awater-soluble heteropolyanion (NH₄)₆P₂Mo₁₈O₆₂. The dried sampleunderwent the same ageing, drying, carbonizing and passivation treatmentas the sample of catalyst Mo-C of Example 3. Catalyst MoP-C4 was thusobtained. XRD analysis revealed that the catalyst contained no carbideparticles with a size greater than 80 Å.

EXAMPLE 8

Catalytic Activity for Tetrahydronaphthalene Hydrogenation

The catalysts of Examples 2 to 7 were tested for tetrahydronaphthalenehydrogenation at a total pressure of 40 bars and for a contact time of0.4 seconds with 0.2 g of catalyst at 300° C. The test feed comprisedtetrahydronaphthalene in n-heptane (nC₇). The partial pressures were asfollows: P_(H2)=30.6 bars, P_(nC7)=9.3 bars, P_(reactant)=0.1 bars. Thecatalytic activity, expressed as the moles of reactant transformed foridentical catalyst quantities was measured after conversionstabilisation.

The results of Table 1 show that the molybdenum carbides supported onalumina containing phosphorous synthesised in Examples 2 to 6 were morehydrogenating than the reference catalyst which contained nophosphorous. Further, the carbides containing phosphorous prepared fromheteropolyanions were more active than the MoP-C1 sample prepared fromammonium heptamolybdate and phosphoric acid.

TABLE 1 Catalytic activity Ref. Catalyst P/Mo (mol/g catalyst/h) Mo-C 06 Mo-S 0 5 MoP-C1 0.4 10 MoP-C2 0.08 9 MoP-C3 0.4 13 MoP-C4 0.11 12

The catalysts of Examples 2 to 7 were then tested using a procedureidentical to that described above except that dimethyldisulphide (DMDS)was added to the test feed so as to obtain a sulphur content of 200 ppmS by weight.

The catalytic activity, expressed in moles of reactant, namelytetrahydronaphthalene, transformed for identical catalyst quantities,was measured after conversion stabilisation.

The results of Table 2 show that the carbides containing phosphorousretained an activity which was higher than that of the referencecatalyst containing no phosphorous when the feed contained sulphur.

TABLE 2 Catalytic activity Ref. Catalyst P/Mo (mol/g catalyst/h) Mo-C 03 Mo-S 0 4 MoP-C1 0.4 5 MoP-C3 0.4 7.5 MoP-C4 0.11 7

EXAMPLE 9

Activity for Hydrodesulphurisation and Hydrogenation of a Gas Oil

The catalysts from Examples 2 to 7 were tested for hydrodesulphurisationof a gas oil which had previously been hydrotreated containing 520 ppm S(feed GO-A) and 135 ppm S (feed GO-B) at a total pressure of 30 bars andat an hourly space velocity of 2.6 h⁻¹ with 40 cm³ of catalyst at 340°C.

The catalytic activity was expressed as the fraction ofsulphur-containing compounds converted (%HDS) for identical catalystquantities and after conversion stabilisation.

The results of Table 3 show that for these hydrotreated gas oilscontaining small quantities of sulphur, the carbonized Mo/aluminacatalysts containing P were better than the catalyst containing no P.

A comparison of the carbonized catalyst containing cobalt with thereference sulphurised CoMo/alumina catalyst shows that it is alsobetter.

TABLE 3 GO-A 520 ppm S GO-B 135 ppm S HDS conversion (%) at HDSconversion (%) at Ref. Catalyst P/Mo 340° C. 340° C. Mo-C 0 18 — Mo-S 012 — MoP-C1 0.4 20 21 MoP-C3 0.4 20 23 MoP-C4 0.11 22 43 CoMoP-C4 0.4 8167 CoMoP-C 0.4 70 56 CoMoP-S 0.4 65 53

The amount of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and the amount ofsaturated hydrocarbons in the gas oil and effluents at 340° C. forhydrodesulphurisation of a hydrotreated gas oil with 135 ppm S are shownin Table 4.

TABLE 4 Saturated hydrocarbon 4,6-DMDBT content content P/Mo (ppm) mol %GO-B 135 ppm S — 25 72.5 MoP-C3 0.4 15 73.8 MoP-C4 0.11 18 73.5 Mo-S 020 73.0 CoMoP-C4 0.11 17 74.8 CoMoP-S 0.4 21 73.8

The results shown in Table 4 illustrate the fact that catalysts based oncarbide convert the refractory compound 4,6-DMDBT(4,6-dimethyldibenzothiophene) better than the sulphide catalystCoMoP-S. Further, the increase in the saturated hydrocarbon content withthe MoP-C3 and CoMoP-C4 carbides also illustrates the improvedhydrogenating power of these catalysts containing group VIB carbide andphosphorous in accordance with the invention.

In conclusion, the catalysts of the invention have better selectivitywith respect to the prior art catalysts.

EXAMPLE 10

Analysis of New and Used Catalysts

This example deals with characterisations obtained before and after thegas oil test with 520 ppm S by elemental analysis (analysis of totalcarbon and sulphur), the results of which are shown in Table 5. Afterthe tests, the catalysts were washed with toluene under reflux (180° C.)prior to analysis then dried overnight at 150° C. in the absence of air.The aim of this operation was to eliminate from the catalyst allhydrocarbon molecules originating from the feed which could remainabsorbed on the support, their presence possibly falsifying the carbonand sulphur analysis after the test.

TABLE 5 C content before C content after S content after Ref. CatalystP/Mo test (weight %) test (weight %) test (weight %) Mo-C 0 0.38 0.430.85 Mo-S 0 0 2.1 6.2 MoP-S 0.4 0 2.4 5.7 MoP-C1 0.4 0.44 0.46 0.7MoP-C3 0.4 0.44 0.49 0.8 MoP-C4 0.11 0.43 0.47 0.6

These results enable the conclusion to be drawn that the carbides ofExamples 3 and 7 do not lose their carbide phase and are not transformedinto the sulphide during the tests, since their sulphur content afterthe test remained far lower than that of the sulphide catalysts Mo-S andMoP-S. This result was also confirmed by the absence of MoS₂ lamellae onthe support surface in the transmission electron microscope exposures.

What is claimed is:
 1. A catalyst comprising at least one amorphoussupport, at least one carbonized metal from Group VIB of the periodictable and phosphorous.
 2. A catalyst according to claim 1, furthercomprising at least one metal from group VIII of the periodic table. 3.A catalyst according to any one of claim 2 in which the group VIII metalis selected from cobalt and nickel.
 4. In a catalytichydrodesulphurisation process comprising contacting a feed with acatalyst at temperatures of 100° C. to 400° C., at an operating pressureof 0.1 to 30 MPa, at a space velocity, expressed as the volume of liquidfeed treated per volume of catalyst per hour, in the range 0.1 to 20 h⁻,with a hydrogen feed ratio, expressed as the volume of hydrogen, in therange 50/1 to 2000/1 the improvement wherein the catalyst is accordingto claim
 2. 5. A catalyst according to claim 1 comprising, in weight %with respect to the total catalyst mass: 10% to 90% of at least oneamorphous support; 0.1% to 30% of a carbide phase containing at leastone group VIB element with formula MxCy where M is at least one groupVIB element and the ratio y/x is in the range 0.75 to 0.25; 0.1% to 10%of phosphorous; 0 to 10% of at least one metal from group VIII of theperiodic table.
 6. A catalyst according to claim 5, in which theamorphous oxide support is selected from transition aluminas, silicas,silica-aluminas.
 7. A catalyst according to claim 6 in which the supporthas a specific surface area in the range 100 to 600 m²/g.
 8. In acatalytic hydrodesulphurisation process comprising contacting a feedwith a catalyst at temperatures of 100° C. to 400° C., at an operatingpressure of 0.1 to 30 MPa, at a space velocity, expressed as the volumeof liquid feed treated per volume of catalyst per hour, in the range 0.1to 20 h⁻¹, with a hydrogen feed ratio, expressed as the volume ofhydrogen, in the range 50/1 to 2000/1 the improvement wherein thecatalyst is according to claim
 7. 9. A catalyst according to claim 7, inwhich the group VIB metal is selected from molybdenum and tungsten. 10.In a catalytic hydrodesulphurisation process comprising contacting afeed with a catalyst at temperatures of 100° C. to 400° C., at anoperating pressure of 0.1 to 30 MPa, at a space velocity, expressed asthe volume of liquid feed treated per volume of catalyst per hour, inthe range 0.1 to 20 h⁻¹, with a hydrogen feed ratio, expressed as thevolume of hydrogen, in the range 50/1 to 2000/1 the improvement whereinthe catalyst is according to claim
 6. 11. In a catalytichydrodesulphurisation process comprising contacting a feed with acatalyst at temperatures of 100° C. to 400° C., at an operating pressureof 0.1 to 30 MPa, at a space velocity, expressed as the volume of liquidfeed treated per volume of catalyst per hour, in the range 0.1 to 20h⁻¹, with a hydrogen feed ratio, expressed as the volume of hydrogen, inthe range 50/1 to 2000/1 the improvement wherein the catalyst isaccording to claim
 5. 12. A catalyst according to claim 1, in which thegroup VIB metal carbide is in the form of particles with a size of lessthan 80 Å.
 13. In a catalytic hydrodesulphurisation process comprisingcontacting a feed with a catalyst at temperatures of 100° C. to 400° C.,at an operating pressure of 0.1 to 30 MPa, at a space velocity,expressed as the volume of liquid feed treated per volume of catalystper hour, in the range 0.1 to 20 h⁻¹, with a hydrogen feed ratio,expressed as the volume of hydrogen, in the range 50/1 to 2000/1 theimprovement wherein the catalyst is according to claim
 12. 14. Acatalyst according to claim 12, in which the group VIB metal is selectedfrom molybdenum and tungsten.
 15. A catalyst according to claim 1 inwhich the group VIB metal is selected from molybdenum and tungsten. 16.In a catalytic hydrodesulphurisation process comprising contacting afeed with a catalyst at temperatures of 100° C. to 400° C., at anoperating pressure of 0.1 to 30 MPa, at a space velocity, expressed asthe volume of liquid feed treated per volume of catalyst per hour, inthe range 0.1 to 20 h⁻¹, with a hydrogen feed ratio, expressed as thevolume of hydrogen, in the range 50/1 to 2000/1 the improvement whereinthe catalyst is according to claim
 15. 17. Preparation of a catalystaccording to claim 1, comprising: a) impregnating a solution into anamorphous oxide matrix, said solution containing at least one group VIBelement, phosphorous and optionally a group VIII element; b) optionally,drying; c) optionally, activating the catalyst in an oxidising orneutral mixture; d) optionally, carrying out a reduction step; e)carbonization with a hydrocarbon; f) optionally, passivating in an inertgas plus oxygen.
 18. Preparation according to claim 17, in which thesources of the group VIB metal are selected from the group formed byoxides, ammonium salts, and salts of heteropolyacids.
 19. Preparationaccording to claim 17, in which the group VIB metal is introduced by asalt of a heteropolyanion containing at least one group VIB element,phosphorous and optionally at least one group VIII element with formulaAxByCzOn where A is at least one group VIB element, B is a group VIIIelement with 0≦y, C is phosphorous and O is oxygen, where the ratioz/(x+y) is between 0.05 and 1.2.
 20. Preparation according to claim 17,in which the hydrocarbons used for the carbonization step are selectedfrom the group formed by alkanes, alkenes, alkynes and aromaticcompounds.
 21. In a catalytic hydrodesulphurisation process comprisingcontacting a feed with a catalyst at temperatures of 100° C. to 400° C.,at an operating pressure of 0.1 to 30 MPa, at a space velocity,expressed as the volume of liquid feed treated per volume of catalystper hour, in the range 0.1 to 20 h⁻¹, with a hydrogen feed ratio,expressed as the volume of hydrogen, in the range 50/1 to 2000/1 theimprovement wherein the catalyst is according to claim
 1. 22. A processaccording to claim 21, in which the feeds contains at least 10% ofaromatic compounds and less than 2000 ppm of S, and is selected from thegroup consisting of kerosines, gas oils from atmospheric distillation,feeds resulting from catalytic cracking, coking, visbreaking, andresidue hydroconversion processes.